Abstract

The disposal of the excessive volume of degraded water coming from agricultural drainage systems is a serious environmental and economic issue, since a significant load of agrochemicals and salts contaminates water bodies downstream. An integrated on-farm drainage management (IFDM) system is an effective method of treatment by successively irrigating zones with drainage water. Each zone is cultivated with crops that have increasing tolerance to salinity, so that the drainage water effluents are minimized to an extent that the final drainage water volume is collected into an evaporation pond. The methodology of the system is proposed herein for a regional irrigation-drainage network (E1 in Agoulinitsa irrigation district in western Greece) as a method of reducing the disposal of agrochemicals in the coastal environment. Based on the design principles of an IFDM system, both the surface area of every irrigation zone and the costs of installing and operating the system are assessed. A scenario regarding the volume of drainage water that must be treated is examined as a sensitivity analysis. The results show that almost 15% of the cultivated area must be bounded for non-productive uses, resulting in a significant economic impact on the net present value of the investment.

INTRODUCTION

The management of drainage water is a major environmental problem where it is the leachate of agrochemicals and salts that are accumulated in the topsoil of agricultural land. Land which has a high water table produces a large volume of drainage effluents, which is itself a major management problem (Westcot 1988). These areas are constantly under the risk of waterlogging and soil degradation, due to the accumulation of salts in the soil profile (Ghorbani et al. 2015; Farid et al. 2017).

The quantitative and qualitative characteristics of drainage water are different, depending on many factors including the method of application, the volume and frequency of the applied irrigation water, the drainage network, the soil properties and the quality of applied water (Rahman et al. 2016). In general it appears degraded, with a high concentration of soluble salts and a significant load of nitrate and phosphate ions (Alexakis et al. 2012). The disposal of this water to a natural watercourse, a lake or a marine ecosystem, contributes to the pollution of the downstream water body.

The integrated on-farm drainage management (IFDM) system was developed in order to confront the disposal of excessive volumes of drainage water that cause salinity and waterlogging problems (Cervinka et al. 2001). In its most sophisticated form, the system was developed in the San Joaquin Valley of California in the late 1980s (CSWRCB 2004), where the dissemination of the general guides and restrictions of the system was part of a large scale water management program. An IFDM system manages irrigation water on salt sensitive, high value crops and sequentially reuses drainage water to irrigate salt-tolerant crops, trees and halophyte plants with increasing tolerance to salinity. A solar evaporator receives the final volume of drainage water; this water evaporates and salt crystallizes. Reservoirs are also used in order to control the imbalance in the supply and demand of water during the irrigation period. The design of these reservoirs along with the evaporation pond is important for calculating the cost of the overall IFDM project, as they affect both the manufacturing cost and the opportunity cost of land occupation.

From the above, it is shown that the application of an IFDM system is environmentally beneficial. From the economic aspect, the sustainability of the system is challenged by the fact that agricultural land is occupied for non-productive uses. For that reason the economic assessment of the investment must take into consideration a variety of parameters, such as land allocation, water prices, crop patterns and fresh water savings. The operating principles of the IFDM system are proposed here for a wider regional irrigation network (the E1 regional network of Agoulinitsa irrigation district in western Greece), upscaling to integrated regional drainage management. A simple methodology is proposed herein that estimates the net present value (NPV) of an IFDM system, requiring minimum input data. Firstly, the allocation of land to the different cultivation stages of the system is estimated according to a practical cropping pattern. The NPV of the investment can then be assessed, since the productive and non-productive land areas are defined. The implementation of an IFDM system could manage the disposal of untreated drainage water to the sea which currently pollutes the Gulf of Kyparrissia with substantial amounts of agrochemicals (Gotsis et al. 2011; Giakoumakis et al. 2013).

METHODS

Allocation of agricultural land

The operating principle of an IFDM system is that drainage water is used for the successive irrigation of plants with increasing tolerance to salinity (Figure 1). Drainage water collected from the cultivation in each stage i, with acreage Ai, is used as irrigation water for the next management level (stage i + 1). Whenever the drainage water is reused, its volume is reduced but also salinity increases (SJVDIP 1999). Depending on the available volume and the quality of the water, IFDM can consist of 1 to n reuse stages. The drainage water collected from the last stage (n) is unsuitable for irrigation and it is wasted in the evaporation pond, covering area Ap.

Figure 1

Operating principle of a 4-stage IFDM system (Source:SJVDIP 1999). Q: discharge; EC: electrical conductivity.

Figure 1

Operating principle of a 4-stage IFDM system (Source:SJVDIP 1999). Q: discharge; EC: electrical conductivity.

Since the allocation of agricultural land to the IFDM stages is not standard, the acreage of each stage, the surface area of the evaporation pond and the required reservoir capacity must be estimated. The total acreage of the IFDM system is:  
formula
(1)
where ΣAi is the sum of the cultivation stages, Ap is the surface area occupied by the evaporation pond, and ΣAr,i is the surface area occupied by the reservoirs.
In each cultivation stage i, the water used for irrigation (AWi) derives from the drainage water collected from the previous cultivation stage (Di-1):  
formula
(2)
where Di-1 is the volume of drainage water collected from the i−1 zone which irrigates the zone i (m3), di-1 is the drainage water discharge (mm), Ai-1 is the area occupied by each cultivation stage (ha). The land area A0 is dedicated to plants sensitive to salinity. AWi is related to the crop water demand and the leaching fraction for each cultivation stage according to the following:  
formula
(3)
where ETi is the crop water demand (mm) and LFi is the leaching fraction in stage i. LFi is determined by the steady-state model described in FAO 29 (Ayers & Westcot 1985). Soil salinity expressed as the electrical conductivity (EC) of the saturated soil paste ECe (dS m−1) is estimated from the salinity of the applied water with the use of a concentration factor (CF):  
formula
(4)
CF can be estimated from a table chart. For simplicity, an equation CF = f(LF) is used produced with the use of regression analysis on the table values (R2 = 0.996):  
formula
(5)
The applicable value of ECe is defined by the targeted crop yield. A simple approximation that is commonly used for modeling the effect of salinity on crop yield (Palangi & Ohmani 2015) is the linear equation of Maas & Hoffman (1977):  
formula
(6)
where RY is the relative yield of the crop, a is the salinity threshold (expressed in dS m−1) and b is the rate at which relative crop yield declines with increasing salinity. Finally application water is estimated with the following equation:  
formula
(7)
The design of the evaporation pond is based on the volume of drainage water collected and the evaporation rate. At the level of preliminary design, Ap (the surface area of the pond, m2), is approximated by the following equation (FAO 1997; Ladewig & Asquith 2012):  
formula
(8)
where Dp = D3 is the volume of drainage water coming from the last reuse zone (m3 d−1), and EVpond is the evaporation rate (m d−1). Considering the reduced evaporation of saline water, Johnston et al. (1997) introduced an empirical coefficient (Cs) that can be applied when the EC of water (dS m−1) ranges between 14 and 60 dS m−1. Thus, Equation (8) is transformed to the following:  
formula
(9)
where ETo is the potential reference evapotranspiration rate (Tanji et al. 2002). Finally, the volume Si (m3) of the reservoir in stage i, within a time range 1 to t is calculated according to the sequent peak method (Bayazit 1982):  
formula
(10)
where Kit is the cumulative deficit for each month t (m3), AWit is the water demand for the month t (m3), Eit is the evaporation from the free surface of the tank (m3) and Vit is the volume of drainage water collected in the area i during month t (m3). When the volume Si is calculated, the surface area of the reservoir Ar,i can also be estimated by dividing with the applicable depth.

Economic framework

The management of an IFDM system has a major restriction regarding the necessity to reduce the drainage outflows. The economic-technical analysis of the system is depressed by this restriction and, in distinction to other drainage water reuse practices, mixing drainage and fresh water is generally excluded. This is because the main objective of the IFDM system is the reduction of the drainage effluents. Coverage of agricultural land for non-marketable crops (halophytes) and also the evaporation ponds reduces the total profit from the land exploitation.

NPV is a useful tool to determine whether a project or investment will result in a net profit or a loss, due to its simplicity. The NPV of an IFDM system estimates the costs and benefits from the agricultural activity in the whole area Atot:  
formula
(11)
where Βi is the total net profit from every stage of cultivation (€), Ci is the total operation cost in every stage (€), r is the annual interest, Βp is the total net profit from the exploitation of the evaporation pond (if it is possible) (€) and Cp is the operation cost of the evaporation pond (€). Ccon is the installation cost of the IFDM infrastructure (€), T is the useful economic life of the IFDM system (years). The total net profit from every stage of cultivation is:  
formula
(12)
where Yi is the crop yield in stage i (kg·ha−1), npi is net profit from each cultivation (€· kg−1) and Ai is the acreage covered by stage i (ha). From Equations (12) and (1) it is shown that the cost-effective region of the IFDM system is the total sum ΣAi which is reduced by the acreage of the reservoirs Ar,i and the evaporation pond Ap.
The operation cost in each Ai subregion is:  
formula
(13)
where FWi is the volume of fresh water used in stage i (m3), pf is the cost of the irrigation water (€ m−3), DWi is the volume of drainage water reused in stage i (m3), pd is the cost of drainage water allocation and reuse (€ m−3) and Cop,i is the remaining cost of operation and maintenance of the network i (€).

Case study

The net irrigated area of the E1 network of Agoulinitsa is 371.3 ha. Surface irrigation is applied (Figure 2). The region is part of an older land reform act carried out in the early 1960s. Farmers rent agricultural land every year, making the land allocation more practical. The total exploitation grade of the irrigation district is almost 80% according to local authorities. Uncultivated land could potentially be used as a part of the non-productive stages of the IFDM system.

Figure 2

Drainage network E1 of Agoulinitsa region.

Figure 2

Drainage network E1 of Agoulinitsa region.

Network E1 and the adjacent E2 were, in the past, part of the technically drained Lagoon of Agoulinitsa and as a result, suffer from a high water table. According to Giakoumakis et al. (2013), the exploitation of the cultivated land in the whole region results in almost 40 tons agrochemicals (mostly dissolved nitrogen and phosphorus), that are disposed of yearly to the sea. Alexakis et al. (2014) showed that soil salinization in Agoulinitsa district could be mainly attributed to salt water intrusion that was mainly detected in the narrow coastline. The drainage water pumping stations cause severe drawdown since the drainage ditches are connected to the aquifer in that area; as a consequence, seawater intrusion is taking place in a zone parallel to the sea shore in the broader area (Karapanos 2009). The spatial variation of drainage water salinity also showed that the coastline is affected by salt water intrusion. The EC ranged between 0.46 dS m−1 and 18.34 dS m−1 (Alexakis et al. 2012). Nevertheless, a significant part of the network is not affected from the salinization, so drainage water and groundwater could potentially be used for irrigation purposes (Gotsis et al. 2015).

According to seasonal water balance (Giakoumakis et al. 2013) the volume of drainage water discharged in the region for the period April to September has very little fluctuation. For this reason, it is considered constant with a mean value of 75.6 mm per month throughout the growing season (453.6 mm overall). It must be stated that in the following analysis the IFDM system is considered to function only for the growing season of April to September. During winter, a high volume of runoff water is discharged through the drainage network, which could be impractical to reuse. It is well documented (Isidoro & Grattan 2011; Rahman et al. 2016) that natural rainfall facilitates salts leaching from the soil profile and therefore diminishes the risk of land degradation to the reuse stages of the IFDM system.

Data for the implementation

In the IFDM system, the quality of drainage water degrades after each recycle. The A0 stage could be irrigated through the established irrigation network with fresh water from the Alfeios river (ECAW = 0.5 dS m−1). As the region is relatively distant from the coastline, it is unaffected by salt water intrusion. According to the mean EC of the drainage water samples (Alexakis et al. 2012) it is practical to consider an average value of 2.70 dS m−1 as the ECAW of stage A1. For the other stages of reuse, the EC of water is assessed according to previous IFDM applications found in literature (SJVDIP 1999; Cervinka et al. 2001; CSWRCB 2004). Thus, drainage water that must be treated in stages A2, A3 and the evaporation pond, has a salinity of 8.0 dS m−1, 12.0 dS m−1 and 25.8 dS m−1, respectively.

The selection of the cultivation in each stage must be based on the cropping pattern in the region in combination with the IFDM requirements. The significant percentage of cotton is advantageous to the suitability of an IFDM system in the region, since it is highly tolerant to salinity. The proposed cropping pattern is shown in Table 1. In the main area A0, maize and alfalfa are selected with a distribution corresponding to the current state. In stage A1 cotton is selected as it is a salt tolerant crop and commonly cultivated in the region as well. In stage A2 salt tolerant forages like tall wheatgrass can be selected, while in stage A3, halophytes and grasses can be grown. Net revenue from these cultivations is considered to be zero since the marketable price could barely meet the annual production cost (Wichelns 2005).

Table 1

Selected cropping pattern in the region according to IFDM cultivation stages

StageCropAcreage (%)Max yielda (kg·ha−1)Net revenuea (€·kg−1)
Α0 Maize 70 13,000 0.20 
Alfalfa 30 10,000 0.20 
Α1 Cotton 100 3,500 0.45 
Α2 Wheatgrass 100 10,000 0.00 
Α3 halophytes 100 10,000 0.00 
Evap. pond – – – -– 
StageCropAcreage (%)Max yielda (kg·ha−1)Net revenuea (€·kg−1)
Α0 Maize 70 13,000 0.20 
Alfalfa 30 10,000 0.20 
Α1 Cotton 100 3,500 0.45 
Α2 Wheatgrass 100 10,000 0.00 
Α3 halophytes 100 10,000 0.00 
Evap. pond – – – -– 

aData from EuroStat database (http://epp.eurostat.ec.europa.eu) for western Greece.

Installation and operation costs of the main infrastructure and equipment required for the operation of an IFDM system are presented in Table 2. The water related costs are also shown, such as the cost of fresh irrigation water and the cost of application of drainage water. The cost of fresh water was accessed through the local water service. Gotsis et al. (2015) estimated that the cost of applying drainage water for irrigation ranged from 1.7 to 3.0 €/103 m3, depending on the elevation. Since it is a flat area a value of 2.0 €/103 m3 is selected. A subsurface-drainage network is proposed as well, designed especially for stages A1-A3 in order to control the water table rise and the efficient leaching of salts from the rootzone. Studies showed that large areas of irrigated lands that suffer from shallow water tables have been covered by such drainage networks to provide favorable conditions for efficient agricultural operation (Ghorbani et al. 2015). The installation, operation and maintenance cost of each stage was derived from the literature (CSWRCB 2004; Wichelns 2005). Τhe useful economic life of the investment is 10 years according to the lifespan of the subsurface drainage network and the evaporation pond.

Table 2

Installation and operation cost of the proposed IFDM system

 Installation costOperation cost
Α0 – – Fresh water price (€/103 m3)a 14.00 
Α1 Pumping station (€)a 40,000 Drainage water application cost (€/103 m3)b 2.00 
Reservoir (€/103 m3)a 3,500 Operation and maintenance (€/ha)c 11.00 
Subsurface drainage network (€/ha)c 900.00 
Α2 Pumping station (€)a 20,000 Drainage water application cost (€/103 m3)b 2.00 
Subsurface drainage network (€/ha)c 900.00 Operation and maintenance (€/ha)c 11.00 
Reservoir (€/103 m3)a 3,500 
Α3 Pumping station (€)a 10,000 Drainage water application cost (€/103 m3)b 2.00 
Subsurface drainage network (€/ha)c 900.00 Operation and maintenance (€/ha)c 11.00 
Reservoir (€/103 m3)a 3,500 
Evaporation pond Installation (€/ha)c 2,200.00 Operation and maintenance (€/ha)c 270.00 
 Installation costOperation cost
Α0 – – Fresh water price (€/103 m3)a 14.00 
Α1 Pumping station (€)a 40,000 Drainage water application cost (€/103 m3)b 2.00 
Reservoir (€/103 m3)a 3,500 Operation and maintenance (€/ha)c 11.00 
Subsurface drainage network (€/ha)c 900.00 
Α2 Pumping station (€)a 20,000 Drainage water application cost (€/103 m3)b 2.00 
Subsurface drainage network (€/ha)c 900.00 Operation and maintenance (€/ha)c 11.00 
Reservoir (€/103 m3)a 3,500 
Α3 Pumping station (€)a 10,000 Drainage water application cost (€/103 m3)b 2.00 
Subsurface drainage network (€/ha)c 900.00 Operation and maintenance (€/ha)c 11.00 
Reservoir (€/103 m3)a 3,500 
Evaporation pond Installation (€/ha)c 2,200.00 Operation and maintenance (€/ha)c 270.00 

aData collected from local authorities.

RESULTS AND DISCUSSION

The computation of the land allocation and the NPV, according to Equations (1)–(12), was made in Visual Basic. The results of the implementation are shown in Table 3. According to this table, the A0 stage occupies an area of 234.73 ha which represents 61.8% of Atot. The acreage of A1, A2 and A3 reuse zones is 89.64 ha, 32.20 ha and 11.89 ha, respectively. The evaporation pond occupies an area of 5.56 ha, which represents about 1.5% of the cultivated area. An estimated total acreage for the reservoirs is 5.14 ha which represents 1.4% of Atot. As a result, the total acreage of the non-productive stages covers 14.7% of the total region.

Table 3

Land allocation and NPV of the proposed IFDM system

StageAcreage (ha)Acreage (%)Reservoir capacity (m3 103)Reservoir acreage (ha)LFiNPV (€· 103)
Αο 229.57 61.8%     
Α1 86.94 23.4% 279.3 3.98 0.05  
Α2 32.20 8.7% 58.8 0.84 0.12 3,080.87 
Α3 11.89 3.2% 22.3 0.32 0.22  
Αp 5.56 1.5%     
StageAcreage (ha)Acreage (%)Reservoir capacity (m3 103)Reservoir acreage (ha)LFiNPV (€· 103)
Αο 229.57 61.8%     
Α1 86.94 23.4% 279.3 3.98 0.05  
Α2 32.20 8.7% 58.8 0.84 0.12 3,080.87 
Α3 11.89 3.2% 22.3 0.32 0.22  
Αp 5.56 1.5%     

The NPV of the IFDM investment with the abovementioned features is equal to 3,080.87 €·103. As a measure of comparison, the NPV of the E1 irrigation network (under the current crop pattern and total exploitation grade of 80%) is estimated to be 4,408.97 €·103. The loss of almost 30% derives mainly from the significant operation and installation cost. Τhis is also exacerbated by the low cost of irrigation water in the region. Fresh water saving does not return as an economic gain with the current prices of irrigation water. Moreover, in the analysis the disposal of drainage water is set to zero, since the water is discharged to the sea without any purification process or treatment. Τhe treatment of drainage water in the San Joaquin Valley, for example, ranges from €228 to €759 per 1,000 m3 (SJVDIP 1999). Thus another environmental benefit of establishing an IFDM system is also not economically accounted for.

The connection between the volume of drainage water that must be reused and the NPV of the IFDM investment was examined as a sensitivity analysis. Drainage discharge ranged from 200–500 mm per season. It is shown (Figure 3) that the NPV of the investment increases significantly when the volume of the drainage water is reduced. It is well documented (FAO 2002; Oster & Wichelns 2014) that the feasibility of the IFDM system is strongly connected to the reduction of drainage water requiring treatment and the further improvement of irrigation methods. Network E1 is a surface irrigation network designed in the early 1960s. The high volumes of drainage water throughout the dry season are caused mainly by updated irrigation practices and secondarily by natural decay of the infrastructure. Under these conditions, the drainage discharges during the irrigation period are maximized, and a highly efficient, robust and costly IFDM system is required.

Figure 3

NPV of the investment in relation to the treated drainage water.

Figure 3

NPV of the investment in relation to the treated drainage water.

CONCLUSIONS

In this study the principles of the IFDM system are analyzed for a regional irrigation network. A simple methodology, requiring minimum input data, is presented that estimates the NPV of the investment. The methodology is then applied in the irrigation network E1 of Agoulinitsa in western Greece, a region in which the reuse of drainage water could manage the disposal problem. The economic analysis showed that the reduction of the cultivated area and the cost of installing and operating the IFDM system cannot be compensated by the fresh water savings under the current water pricing. A loss of almost 30% of the NPV of the current network is estimated, which derives from the suspension of the agricultural land for non-productive uses and the change in the crops pattern. The sensitivity analysis showed that the NPV of the investment is disproportional to the volume of the drainage water that must be treated. Finally, for the network E1 of Agoulinitsa, the most viable solution is a comprehensive upgrade of the current irrigation and drainage network which could then implement an IFDM system. This option could maximize fresh water savings (coming from an updated irrigation network and the reuse of drainage water) and minimize the drainage effluents that must be treated. Under these conditions, the application of the IFDM system could eliminate the load of agrochemicals that is disposed of in the coastal environment.

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